This invention relates to a magnetic bearing system for a rotor which consists of a magnetizable material and which, in its axial direction, is suspended by means of an axially magnetized permanent magnet ring which surrounds it and, in the radial direction, is stabilized by means of electromagnetic devices which are arranged around it in a ring shape and which can be excited by means of an electronic control device which is connected with sensors which detect the radial deviations of the rotor.
A magnetic bearing system of the initially mentioned type is known (Lecture by Karl Boden "Wide-Gap, Electro-Permanent magnetic Bearing System with Radial Transmission of Radial and Axial Forces", on the occasion of a symposium from Jun. 6 to Jun. 8, 1988 in Zurich). In the case of the known magnetic bearing system, the rotor is suspended in the axial direction by means of an axially magnetized permanent magnet ring. An active radial stabilization is provided in addition to this passive axial bearing. This radial stabilization comprises electromagnetic devices in the form of segmental coils which are disposed in pairs opposite one another and interlinked and have a common ring-shaped core which surrounds the rotor. The segmental coils, which generate radially directed magnetic fields, can be excited by way of an electronic control device to which sensors are connected which detect radial position deviations of the rotor. The signals of these sensors are analyzed in order to excite the segmental coils such that radial stabilizing forces are obtained. The known magnetic bearing system is used in such a manner that a stator of an electric motor is arranged between two magnetic bearing systems of this type and drives the magnetically disposed rotor.
It is an object of the invention to open up a new field of application for the known magnetic bearing system.
This object is achieved in that the rotor is an essentially cylindrical sleeve which is constructed as a balloon limiting device which can be carried along by a yarn and is arranged centrically with respect to a spinning or twisting spindle.
The invention is based on the recognition that, by means of a magnetic bearing system of the initially mentioned type, it is not only possible to provide the bearing for rotors driven by an electric motor but also for a sleeve, although this sleeve is driven by the carrying forces of the yarn which act not only in the circumferential direction but also have a radial force component. The active stabilization in the radial direction generates sufficiently high forces in order to keep the sleeve centered with the required precision. The suspended sleeve can therefore be disposed in a non-contact manner.
In an advantageous development of the invention, it is provided that the sleeve is disposed independently of a disk which rotates along with the spindle. As a result, it is possible to provide a balloon limiting device for a double spinning or twisting spindle which is independent of the disk and rotates independently of the disk, being taken along by the frictional force of the yarn.
Co-rotating balloon limiting devices are known in the case of double twisting spindles (Swiss Patent Document CH-PS 417 418, German Patent Document DE-PS 27 00 820), but, in the case of these types of constructions, the balloon limiting devices are fixedly mounted on the rotating disk so that they rotate together with this disk.
In the case of long sleeves, as they are required for double twisting spindles for use as balloon limiting devices, it is provided in an expedient development of the invention that the sleeve is magnetically disposed in the area of its two front ends.
In another embodiment of the invention, it is provided that the sleeve, which is used as the balloon limiting device, is arranged above a ring spindle.
It is known to provide a co-rotating balloon limiting device in the case of ring spindles (French Patent Document FR-A 24 5 888) which is aerostatically disposed. However, this type of a bearing has not been successful in machines in practice which is probably mainly the result of the risk of fly existing in spinning plants.
In the case of this type of a balloon limiting device, which has only a small axial dimension, a single magnetic bearing system is sufficient which is then expediently arranged essentially centrically with respect to the sleeve.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.